Yanmar vs Cumnins

I am looking to replace my 390 lost to Sandy with a 400, one of my biggest question are the engines mainship used. Some of the boats I look at in florida have a cummins 380 QSB5.9 and othersYanmar 6LYA-STP. What is the exprience of users of these engine, are they mech or electronic control, does that make a diffence in opertations cruising, I used to service the3016 on my old boat are these harder to service. My cruising speed is in the 7.5 k Which of these engines have the least problems, good fuel economy,and how would you rate the manufactures support when there is a problem

stepheniser

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The QSB is a modern, electronic, common rail engine. It doesn't smoke and is quiet. The Yanmar is a sophisticated, all mechanical engine. Either will run fine at low speeds.

Each have their plusses and minuses. The Cummins has a weak rw pump and a fussy after cooler, but has a rock solid lower end.

David

I'd suggest you post the same question on boatdiesel.com There are some great resources (D Marchand above being one) there to answer the question with some located in FL that you could talk to direct in more detail. As you likely know, Mainship exhaust and shower head installs were not always the best with potential for #6 cylinder salt water ingestion. No matter whose engine, look this area over very carefully. In both cases, prior recorded maintenance especially around the HX and after coolers, or lack thereof, is a factor to consider also.

Al things equal, I'd go Cummins.

I'd say it is a toss up. They are both excellent engines. My only issue with Cummins in my dail(even hourly) visits to Yachtworld, is that it seems that many Cummins powered boats have had one or both engines rebuilt on used boats. And usually with not a lot of time on them. I don't know if they are cheap to rebuild and people do it for preventative reasons. Another thing is my wife works for a yacht service business. I have asked the techs there if they have ever seen a Cummins with it's "guts" hanging out of the side. The answer was yes on more than one occasion. I asked the same about Yanmar and the answer was NO.

If you are gonna run at slower speeds, then I would be weary of neither. If you are going to run at planing speeds and up in the higher range of the power band, I personally like Yanmar.... Just an opinion.

stepheniser said:

Which of these engines have the least problems,

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Google Cummins problems and then Yanmar problems. It would seem that both have their share of problems. (As do any diesels.)

SeaHorse II said:

Google Cummins problems and then Yanmar problems. It would seem that both have their share of problems. (As do any diesels.)

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That they do Walt! Good to see you around here. While I am a Yanmar operator currently, there is a good chance I will be a Cummins operator in the not so distant future and am totally fine with that!!!....looking forward to it actually.

Baker said:

I'd say it is a toss up. My only issue with Cummins in my dail(even hourly) visits to Yachtworld, is that it seems that many Cummins powered boats have had one or both engines rebuilt on used boats. And usually with not a lot of time on them. I don't know if they are cheap to rebuild and people do it for preventative reasons.

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What I found having replaced more than one Cummins engine in a boat is that there are a high percentage of engines being replaced due to overpropping by the boat builder. There is a strong incentive for builders to overprop, speed sells boats.

Another reason is lack of maintenance, specifically after cooler and heat exchanger maintenance.

Here's a good example, my boat. I have a Bayliner 4788. From the factory it came with 330 HP Cummins 6BTA5.9L diesels. It also came with 24X24 props.

The day the boat weas brand new, with little fuel and no owners junk on board the boat would make its rated WOT of 2800 RPM. Add full fuel, water, a skiff, and all the owners stuff and theres no way the boat would make 2800 RPM.

So, the PO of my boat not realizing he was overpropped drove the boat hard, at high RPMs (Cummins used to recommend running at WOT -200 RPM for a cruise speed). He also did not perform his preventative maintenance on the engine heat exchangers and aftercoolers. Well, a thousand hours later one engine had high blow by and the other was marginal.

When I repowered the boat with new factory reman Cummins engines I reduced the prop pitch from 24" to 22". I can make 2850-2900 RPM with a full loadout, my EGT is running <900 and my boost at a 2400 RPM cruise is around 12 lbs.

Out of curiosity, how much does it cost for factory remans??? Motor only and then total job...if you don't mind me asking. You can PM me if you want. The reason I ask is I may be driving a Cummins powered boat before too long.

Baker said:

Out of curiosity, how much does it cost for factory remans??? Motor only and then total job...if you don't mind me asking. You can PM me if you want. The reason I ask is I may be driving a Cummins powered boat before too long.

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The engines were about $16K each after the core charge was refunded.

The engine swap was around $50K I think. I'm putting it that way because I had allot of other work done at the same time, and some things made sense to do while the engines were out.

for example, the biggest issue with the 4788 engine room is access to the outboard side of the starboard engine. I have no clue why but Bayliner installed the waste tank there making access all but impossible. I had the waste tank removed and had a Raritan Hold-N-treat installed in the foward part of the engine room. This fixed the access issue and provided onboard waste treatment as well.

Another thing we did was to replace all of the engine instruments in the pilothouse. The boat now has boost and egt gauges along with Aetna digital tachs.

The list goes on and on, it was a total ground up refit.

Damn!!! Looks nice!! Thanks for sharing the information!!!